Perspectives on the reuse of fly ash and phosphogypsum in civil engineering

Fly ash and phosphogypsum are industrial waste materials abundantly available in South Africa and worldwide. The staggering increase in the use and disposal of fly ash and phosphogypsum has motivated research to expand its reuse in construction to minimise the extraction of virgin materials

Setting Time and Workability of Geopolymerized Fly Ash-Phosphogypsum Paste and Mortar

Geopolymer is no longer viewed as a concept for a greener society but rather as a pragmatic solution for reducing CO2 emissions in the construction industry. It is commonly produced using industrial waste materials such as fly ash (FA) and phosphogypsum (PG). Globally, FA has an estimated annual production of around 1 billion tonnes and that of phosphogypsum is around 300 million tonnes, of which utilization stands at 50% and 15% of the total generated, respectively [1]. Geopolymers have been extensively studied as an alternative to ordinary Portland Cement (OPC) [2], [3] but to date, no study has been done to investigate the setting time and workability of geopolymerized fly ash-phosphogypsum paste and mortar. This research investigates the setting time and workability of geopolymerized fly ash-phosphogypsum paste (GPP) and mortar (GPM) using a Vicat needle procedure per ASTM C191 and the flow table test per ASTM C1437, respectively. The materials used were PG, Class F FA, silica sand, NaOH pellets of 99% purity, and Na2SiO3 solution of the composition Na2O = 8.3%, SiO2 = 27.7%, H2O = 64%, and Ms (SiO2/Na2O) = 3.34. The dissolution of NaOH pellets in water is an exothermic process [4] therefore the prepared NaOH solution was kept in a sealed glass bottle for 24 hours at room temperature to allow sufficient cooling before mixing with the Na2SiO3 solution. The specimens were prepared at 10M NaOH + Na2SiO3 Ms of 3.34, Na2SiO3/ NaOH ratio of 1.5, Alkaline Liquid/Precursor ratio of 0.4, Binder/Aggregate ratio of 1.0, and varying PG at 10 wt% increments. As per ASTM C305 for mixing pastes and mortars, the preparation of the specimens started with dry mixing the FA with PG in a conventional pan mixer for 3 minutes, followed by the gradual addition of alkaline solution and wet mixing for 5 minutes. Soon after wet mixing, the manufactured paste and mortar were tested for setting time and workability. It was found that an increase in the PG wt% led to a decrease and/or acceleration in the initial setting time (INSET) and final setting time (FINSET) attributed to the rapid dissolution of Ca2+ in low alkaline concentrations outnumbering that of Al3+ and Si4+ and thus forming ettringite and C-A-S-H gel that facilitates hardening shortening the setting time [5], [6]. The INSET of GPP decreased from 37 min (at 10wt% PG) to 27 min (at 30 wt% PG) while the FINSET of GPP decreased from 155 min (at 10wt% PG) to 125 min (at 30 wt% PG). The INSET of GPM decreased from 29 min (at 10wt% PG) to 23 min (at 30 wt% PG) while the FINSET of GPM decreased from 142 min (at 10wt% PG) to 113 min (at 30 wt% PG). Furthermore, the workability of GPP and GPM decreased with an increase in PG wt% attributed to faster hydration activity, accelerated setting, and increased viscosity. The workability of GPP decreased from 176 mm (at 10 wt% PG) to 138 mm (at 30 wt% PG) while that of GPM decreased from 137 mm (at 10 wt% PG) to 112 mm (at 30 wt% PG). The development of GPP and GPM offers a sustainable circularity construction solution to minimize OPC usage and prevent the disposal of FA and PG in landfills. Future research should investigate the mechanical properties of GPP and GPM

Public Perception of Solid Waste Management Practices in Nigeria: Ogun State Experience

The effects of poor solid waste management practices in many developing countries have been identified in the literature. This study focuses on understanding the public perception and attitudes of people towards local waste management practices. Five Local Government Areas in Ogun State, Nigeria, were selected based on population, landmass, spatial location, and distribution. The study used a survey that looked into the socio-demographics, household characteristics, and standard solid waste disposal practices at the household and municipal levels. Factors such as frequency of waste collection, presence of environmental task force/protection agency, and level of effectiveness of such task force/agency were all investigated. The study verified the impact of people’s attitudes towards waste management, as well as the effects of monitoring and control on the management of waste. The results showed that significant factors such as age, income, and education levels affect the perceptions, practices, and attitudes of the people towards solid waste management. An average of 36.6% of the people in the selected local governments dispose of their solid wastes at open dumps, with the majority of the residents (54.4%) still with the opinion that sanitation services are too costly and should be the prerogative of the local and state governments to carry out. These outcomes resonate that more efforts by the government and relevant stakeholders should be put into proper enforcement of environmental laws, as well as creating awareness on proper solid waste management practices in schools and public places

Evaluation of the Influence of Reactor Design on the Treatment Performance of an Optimized Pilot-Scale Waste Stabilization Pond

ABSTRACT Waste stabilization pond (WSP) is globally one of the most popular wastewater treatment options due to its high efficiency and low cost. A field scale prototype was designed and scaled down to a pilot-scale model using dimensional analysis in the development of the foot print size. Pilot-scale reactors were built with the specifications produced from literature suggested reactor geometric configurations and experimental study was conducted to evaluate the performance of optimized pilot-scale WSP configurations. The optimized pilot scale WSPs consisted of an anaerobic, facultative, and a maturation stage with varying baffle orientation, length to width ratio, and depth. Comparisons were made on the optimized pilot-scale WSP reactors. The removal performance of the experimental test was based on a number of parameters (Faecal coliform, pH, TDS, and Conductivity). Results showed that the significantly lower cost design displayed slightly better removal performance compared to other WSP design developed from literature data. This paper covers a relevant subject within the field of waste stabilization ponds, namely the representation of the influence of reactor design on the treatment performance of WSP